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The town is 45 minutes south of San Francisco, and less than 20 minutes to the headquarters of Facebook, Google and most of the major tech companies in Silicon Valley.

Atherton is the most expensive real estate ZIP code in the United States. The average home price has soared close to 40 percent year over year, according data compiled by several Silicon Valley real estate agencies.

Real estate brokers say there was a frenzy of buying for homes in the $5 million range last year, but this year demand is shifting to the more expensive houses. In the first quarter of 2014, there were seven sales of mansions in Atherton in excess of $10 million, some to deep-pocketed Chinese buyers.

"We have a market here with high demand, low supply. And of course we are the center of technology. The tech sector is doing well. Everything that drives the tech sector, the local economy, venture capital, private equity. We're just the center of innovation here. So that, more than anything, drives our housing market," said Tom LeMieux of Pacific Union International, a real estate firm.

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